New Part Day: Lynxmotion Smart Servos

Anyone who shops for robotics kits would have come across a few designed by Lynxmotion. They’ve been helping people build robots since 1995, from robot arm kits to hexapod chassis and everything in between. We would expect these people know their motors, so when they launched their own line of servo motors called Lynxmotion Smart Servos (LSS), it is worth spending a bit of time to look over what they offer.

While these new devices have a PWM mode compatible with classic remote control servos, unleashing their full power requires bidirectional communication over a serial bus. We’ve previously given an overview of three serial bus servos already on the market for comparison. A quick look at the $68-$100 price tags listed on Lynxmotion’s parent company RobotShop made it clear they do not intend to compete on price, so what interesting features do these new kids on the block have?

Digging into product documentation found some great details. Acceleration and deceleration rates are adjustable, which can help with smoother robot movement. There’s also an adjustable level of “stiffness” that adds some “give” (compliance) so a robot won’t have to be as stiff as… well, a robot!

Mechanically, the most interesting internal component is the magnetic position sensor. They are far more precise than potentiometers, but more importantly, they allow positioning anywhere within full 360 degrees. Many other serial bus servos are constrained to positions within an arc less than 360 degrees leaving a blind spot.

An interesting quirk of the LSS offerings is that the serial communication protocol uses human-readable text characters, so sending a number 255 means transmitting a three byte string ‘2’, ‘5’, and ‘5’ instead of single byte 0xFF. This would make debugging our custom robot code far easier, at the cost of reduced bandwidth efficiency and loss of checksum for detecting communication errors. It’s a trade-off that some robot builders would be happy to make, but others might not.

Externally, these servos have bountiful mounting options including some we didn’t know to ask for. Historically Lynxmotion kits have used a wide variety of servo mounting brackets, so they are motivated to make mechanical integration easy. The most novel offering is the ability to bolt external gears to the servo body. A set of 1:3 gears allow for gearing the servo up or down, or you can use a set of 1:1 gears for a compact gripper.

As you’d expect of servos in this price range, they all have metal gears, but they also have the ability to power the motor directly from a battery pack (a 3 cell lithium polymer is recommended). There are additional features, like an RGB LED for visual feedback, which we didn’t cover here so dig into the documentation for more. We look forward to seeing how these interesting little actuators perform in future robotics projects.

Wrangling RC Servos Becoming A Hassle? Try Serial Bus Servos!

When we need actuators for a project, a servo from the remote-control hobby world is a popular solution. Though as the number of servos go up, keeping their wires neat and managing their control signals become a challenge. Once we start running more servos than we have fingers and toes, it’s worth considering the serial bus variety. Today we’ll go over what they are and examine three products on the market.

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Evolving The 3D Printed Linear Actuator

Our open source community invites anyone with an idea to build upon the works of those who came before. Many of us have encountered a need to control linear motion and adapted an inexpensive hobby servo for the task. [Michael Graham] evaluated existing designs and believed he has ideas to advance the state of the art. Our Hackaday Prize judges agreed, placing his 3D Printed Servo Linear Actuator as one of twenty winners of our Robotics Module Challenge.

[Michael]’s actuator follows in the footstep of other designs based on a rack-and-pinion gear such as this one featured on these pages, but he approached the design problem from the perspective of a mechanical engineer. The design incorporated several compliant features to be tolerant of variances between 3D printers (and slicer, and filament, etc.) Improving the odds of a successful print and therefore successful projects. Beginners learning to design for 3D printing (and even some veterans) would find his design tips document well worth the few minutes of reading time.

Another useful feature of his actuator design is the 20mm x 20mm screw mounting system. Visible on either end of the output slider, it allows mixing and matching from a set of accessories to be bolted on this actuator. He is already off and running down this path and is facing the challenge of having too many things to share while keeping them all organized and usable by everyone.

The flexible construction system allows him to realize different ideas within the modular system. He brought one item (a variant of his Mug-O-Matic) to the Hackaday + Tindie Meetup at Bay Area Maker Faire, and we’re sure there will be more. And given the thoughtful design and extensive documentation of his project, we expect to see his linear servos adopted by others and appear in other contexts as well.

This isn’t the only linear actuator we’ve come across. It isn’t even the only winning linear actuator of our Robotics Module Challenge, but the other one is focused on meeting different constraints like compactness. They are different tools for different needs – and all worthy additions to our toolbox of mechanical solutions.

Stepper Motor Robot Arm Has Smooth Moves

[Tobias Kuhn] had watched a YouTube video about a robot arm which used servo motors, and wanted to try making one himself. But he found it hard to get slow or smooth movements out of the servos. Even removing the microcontroller and trying to work with the servo’s driver-IC and potentiometer from an Arduino Nano didn’t get him satisfaction.

Then he found the very affordable 28BYJ-48 stepper motor. After some experimenting, he came up with a smooth moving robot arm with four steppers controlled from an Arduino Mega and A4988 stepper motor drivers. Rather than write a bunch of stepper motor code himself, he installed and ran a four-axis fork of grbl on the Arduino, turning it into a stepper motor controller. One minor hitch was that the A4988 motor drivers are for bipolar stepper motors but 28BYJ-48 steppers are unipolar. Luckily he knew of a very simple hack which our [Brian Benchoff] wrote about for turning a unipolar motor into a bipolar motor.

To tell the robot arm what to do, he built a replica arm with potentiometers in place of the stepper motors. As he manipulates the replica, the values of the potentiometers are read by a Raspberry Pi and some custom Python code which sends the appropriate G-code to the Arduino/grbl controlled robot arm. There’s a bit of a lag but when he moves the replica arm, the robot arm does the same move. See it in action in the video below.

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Robot Hand Goes Wireless

We can’t decide if [MertArduino’s] robotic hand project is more art or demonstration project. The construction using springs, fishing line, and servo motors isn’t going to give you a practical hand that could grip or manipulate anything significant. However, the project shows off a lot of interesting construction techniques and is a fun demonstration for using nRF24L01 wireless in a project. You can see a video of the contraption, below.

A glove uses homemade flex sensors to send wireless commands to the hand. Another Arduino drives an array of servo motors that make the fingers flex. You don’t get fine control, nor any real grip strength, but the hand more or less will duplicate your movements. We noticed one finger seemed poorly controlled, but we suspect that was one of the homemade flex sensors going rouge.

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The Cicada: A Parasite Art Piece With Commitment Issues

How often do you think deeply about the products around you? How about those you owned five years ago? Ten? The Cicada — brainchild of [Daniel Kerris] — is an art piece that aims to have the observer reflect on consumer culture, buyer’s remorse, and wanting what we cannot have.

The Cicada consists of an ultrasonic sensor feeding data to a Raspberry pi which — calculating the distance of an approaching human — either speeds up or slows down a servo motor connected to a General Electric Walkman’s cassette speed potentiometer. Upon detecting someone approaching, The Cicada begins to loop the chorus of Celine Dion’s “I Will Always Love You”. As you move closer, the tape speed slows, and there is a transition from love at first sight to nightmarish drawl as the music slows.

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Robotic Arm From Cardboard

Google showed the world that you could make a virtual reality headset from cardboard. We figure that might have been [Uladz] inspiration for creating a robotic arm also made out of cardboard. He says you can reproduce his design in about two hours.

You’ll need an Arduino and four hobby servo motors. The cardboard doesn’t weigh much, so you could probably use fairly small motors. In addition to the cardboard, there’s a piece of hardboard for the base and a few metal clips. You can control it all from the Arduino program or add an IR receiver if you want to run it by remote control. There’s a video of the arm–called CARDBIRD–in action, below.

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